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UNIVERSITY    OF     ILLINOIS    LIBRARY    AT    URBANA-CHAMPAIGN 


UNIVERSITY  OF  ILLINOIS  BULLETIN 

Vol.  VI  APRIL.  5,  1909  No.  25 


LEntered  February  14,  1902,  at  Urbana,  Illinois,  as  second-class  matter 
under  Act  of  Congress  of  July  16th,   1894.] 


BULLETIN  No.  10,  DEPARTMENT  OF  CERAMICS 

C.    W.    ROLFE.    Director 


A  METHOD  MAKING  POSSIBLE  THE  UTILIZATION 
OF  AN  ILLINOIS  JOINT  CLAY 

BY 
A.  V.  BLEININGER  AND  F.  E.  LAYMAN 


AN  ATTEMPT  TO  DETERMINE  THE  AMOUNT  OF  HEAT 

UTILIZED  FROM  A  DOWN-DRAFT  KILN  BY 

THE  WASTE  HEAT  DRYING  SYSTEM 


By  A.  V.  BLEININGER 


1908-1909 


PUBLISHED  FORTNIGHTLY  BY  THE  UNIVERSITY 


AN   ATTEMPT   TO  CALCULATE   THE  AMOUNT   OF 

HEAT  UTILIZED  FROM  A  DOWN-DRAFT 

KILN    BY    THE    WASTE    HEAT 

DRYING  SYSTEM.* 

BY 

A.  A'.  Bleininger. 


In  a  test  made  some  time  ago  the  heat  distribution  of 
a  down-draft  kiln  employed  for  burning  hard  building 
brick  was  calculated,  based  upon  careful  measurements  of 
the  kiln  and  exit  temperatures,  the  composition  of  the 
waste  uases,  the  fuel  and  the  asbes,  together  with  the 
weight  of  the  coal  and  of  the  ware.  The  result  was 
summarized  as  follows ; 

Heat  lost  by  the  fuel  gases 27.:^', 

Theoretical   Heat  required  to  burn 

the  bricks ....19.55^ 

Heat  lost  by  unburnl  carbon  in  ash..  :>.r>l', 

I  leaf  taken  up  by  kiln  and  lost  by 

radiation '.....49.G1% 

At  the  close  of  the  burn  a  30-inch  goose-neck  was 
inserted  into  the  door  of  the  kiln  which  connected  with  an 
underground  flue  leading  to  the  dryer.  The  air  was  thus 
drawn  from  the  kiln  by  means  of  the  large  fan  located  at 
the  dryer.  A  draft  gauge  was  then  connected  with  the 
^■oose-neck  for  determining  the  "head"  caused  by  the  pull 
of  the  fan.  This  was  found  to  be  quite  uniform  and  equal 
to  14  divisions  of  the  Richardson-Lovejoy  petroleum  gauge 
which  corresponds  to  about  14  inch  of  water  by  actual 
measurement.  A  thermo  couple  was  likewise  inserted  into 
the  goose-neck  which  was  replaced  later  by  thermometers. 

*Read  at  the  Annual  Meeting  of  the  American  Ceramic  Society   Rochester,    N.    Y., 
Feb.  lst-3rd,  1909 


Iii  this  manner  the  temperature  of  the  air  leaving  the  kiln 
was  carefully  measured  for  108  hours. 

In  attempting-  to  calculate  the  amount  of  heat  ex- 
hausted from  the  kiln  by  means  of  the  fan  we  must  know 
first  the  velocity  of  the  air  through  the  pipe.  This  it  was 
only  possible  to  approximate,  since  the  draft  gauge  was  not 
calibrated  against  an  anemometer.  The  final  value  of  the 
velocity  accepted  is  lower  than  the  actual  velocity, 
since  no  attempt  was  made  to  use  the  Pitot  tube  cor- 
rection factor,  which  is  greater  than  unity.  The  theo- 
retical velocity  calculated  from  the  head  shown  by  the 
gauge,  giving  a  lower  value  was  hence  used,  neglecting  the 
decrease  in  the  viscosity  of  the  hot  air  and  other  factors 
due  to  cooling  between  the  kiln  and  the  fan.  This,  it  is 
believed,  did  not  introduce  any  significant  error,  since  evi- 
dently the  velocity  was  fairly  uniform  throughout  the  test. 
The  velocity  is  thus  calculated  from  the  formula. 

V=  V2    jr.    h    

d2 
v  =  velocity  in  meters  per  second. 
g  =  gravity  constant  =  9.8  m. 
h  =  head  of  water,   expressed   in 

meters  =  0.00  -  m. 
d,=  density  of  air  at  0°   C. 
d._.=  density  of  water  at   0°   C. 

substituting  we  have 

v  =  VKU5     '.     0.006     '.     772  =  9.4(3   m. 

The  velocity  of  the  air  was  taken   to  be  !>..">  in.    per 

second. 

The  time  was  divided  into  nine  periods  of  12  hours 
each  and  the  mean  exit  temperature  calculated  for  every 
period.     These  were  found  to  be  as  follows : 

0—  12  hours  885°  C. 

12—  24  hours  715° 

24  —  36  hours 640° 

30  —  48   "  540° 

48—  60   "  : 435° 

60—  72   " 355° 

72—  S4   " 265° 

84—  96   " 185° 

96—108   " 135° 

With  a  pipe  diameter  of  30  inches  and  using  the  velo- 
city above  calculated  we  have  a  discharge  of  4.18  en.  in. 
per  second  or  of  180,576  en.  in.  during  12  hours.  Owing 
to  the  fact  that  the  test  was  carried  on  during  the  dryest 


and  hottest  part  of  the  summer,  with  an  average  tempera- 
ture of  about  20°,  the  humidity  approximated  at  50%. 
This  figure  is  purely  a  guess,  since  the  hygrometer  was 
found  to  have  been  broken  during  transit.  However,  the 
introduction  of  the  atmospheric  moisture  factor  is  not  an 
important  one,  numerically.  Assuming  a  vapor  tension 
of  8.7  mm,  the  volume  of  steam  introduced  for  the  volume 
of  air  given  above  would  be  21194  eu.  m.  The  barometric 
pressure  was  taken  to  be  750  mm. 

There  remains  now  to  calculate  the  weights  of  air  and 
steam  taken  through  the  pipe  for  each  period  as  well  as  the 
heat  removed.  This  is  illustrated  for  the  first  period  as 
follows  :• 

273 

Air....l80576 .  1.27.")  .  865  .  0.237=11,127,000  kg.  Cals. 

27.3    -   885 
27:5 

Steam..  2094 .  0.797  .  865  .  0.48=   103,300  kg.  Cals. 

273    +   885  — 

Total    heat   removed    by   air  and    steam        11,290,300  kg.   Cals. 

In  this  calculation  0.237  and  0.48  are  the  specific  heats 
of  air  and  steam  respectively.  Tabulating  the  results  we 
obtain  : 

Period  Total   number  of  kg.  Calories 

1 11,290,300 

2        10,032,820 

:;         10.264.ol0 

4 9.067,880 

5 8,858,130 

(i         8.003,050 

7 6,883,290 

8 5,444,750 

!>  4,260,190 

Total 75,364.980   kg.   Cals. 

The  coal  used  during  the  burn  had  a  calorific  value 
of  6200.  Hence  the  weight  of  coal  equivalent  to  the 
amount  of  heat  drawn  from  the  kiln  would  be 

74     462     308 

=12155  kg. "or 

6200 

20,741  pounds.  During  the  entire  burn  95,045  pounds  of 
coal  were  used.  The  heat  exhausted  from  the  kiln  during 
cooling  then  equals  28.1%  of  the  total  heat  introduced,  so 
that  the  heat  distribution  could  be  rearranged  as  follows : 


Heat  lost  by  flue  gases 27.33% 

Theoretical   heat  required  to  burn 

the  ware :...  19.55% 

Heat  lost  by  imburut  carbon  in  ash  3.51% 
Heat  stored  by  kiln  and  ware  and 

recovered  for  drying  purposes....  28.10% 
Heat  lost  by  radiation  and  left  in 

kiln  and   ware  unused 21.51% 


100.00% 
The  recovered  heat  thus  amounts  to  the  equivalent  of 
practically  400  pounds  of  coal  per  thousand  bricks,  or 
speaking  more  correctly,  about  130  pounds  of  coal  per  ton 
of  burnt  clay,  which  is  more  than  the  heat  theoretically  re- 
quired to  burn  the  bricks.  It  is  evident  that  not  all  of  this 
heat  is  used  in  drying  bricks,  some  of  it  is  lost  on  the  way 
to  the  dryer  and  in  the  latter  itself.  That  a  considerable 
amount  of  the  heat  is  derived  from  the  hot  kiln  walls  is 
apparent  from  the  comparison  of  the  figures  in  the  final 
distribution.  Owing  to  the  fact  that  this  test  was  carried 
on  in  summer,  the  results  show  the  most  favorable  condi- 
tions under  which  this  particular  kiln  operates.  In  winter 
the  heat  actually  available  for  drying  would  be  consider- 
ably less,  owing  to  the  increased  loss  by  radiation  during 
cooling. 


A  METHOD  MAKING  POSSIBLE  THE  UTILIZATION 
OF  AX  ILLINOIS  JOINT  CLAY.* 

BY 

A.  V.  Bleiningek  and  F.  E.  Layman. 

A  large  part  of  Northern  and  Central  Illinois  is  cov- 
ered by  the  so-called  joint  clays  which  arc  of  glacial  ori- 
gin and  vary  in  depth  from  one  to  five  feet.  These  (days  are 
weathered  to  different  depths  and  in  this  condition  they 
form  the  basis  of  a  considerable  brick  industry.  They  are 
red-burning  surface  clays,  extremely  fine  in  "rain, 
but  as  is  characteristic  of  glacial  deposits,  admixed  with 
mineral  detritus  of  all  kinds.  In  a  number  of  localities, 
however,  they  are  quite  uniform  in  composition  for  consid- 
erable areas  ami  free  from  excessive  amounts  of  rock  de- 
iiris,  gravel,  etc. 

In  the  weathered  condition  they  usually  work  up  quit" 
well  into  bricks  and  tiles  though  they  are  sometimes  liable 
to  check  in  burning.  Some  distance  below  the  surface, 
however,  they  are  apt  to  show  a  peculiar  behavior  in  dry- 
ing, giving  rise  to  characteristic  splitting  and  cracking'. 

When  made  into  bricks  they  split  through  vertically 
into  more  or  less  regular  cubes,  the  same  thing  being  ob- 
served when  a  bank  is  stripped  and  the  surface  is  drying 
out.  The  loss  arising  from  this  peculiarity  in  attempting 
to  make  clay  products  out  of  this  material  is  quite  con- 
siderable, since  the  checking  occurs  in  the  drying  as  well 
as  in  the  burning,  the  latter  being  due  probably  to  incipi- 
ent cracks. 

A  typical  deposit  of  this  character  is  found  on  the 
land  of  Mr.  J.  W.  Stipes,  close  to  the  city  of  Urbana,  111. 
This  clay  is  extremely  line  grained,  red  burning,  very 
sticky  and  plastic  but  not  high  in  bonding  power.     Within 

*Read  at  the  Annual  Meeting  of  the  American  Ceramic  Society,    Rochester,    N.  Y., 
Feb.  lst-3rd,  1909 


a  foot  of  the  surface  it  has  been  (■hanged  by  weathering  so 
that  it  does  not  show  the  peculiarity  mentioned  above  to  a 
striking  degree  but  at  a  somewhat  greater  depth  its  true 
joint  structure  appears.  There  arc  no  differences  in  color 
noticeable  between  the  weathered  and  the  unweathered  por- 
tion, both  are  of  about  the  same  yellow.  The  clay  is  com- 
paratively free  from  mineral  debris  and  stands  up  remark- 
ably well  in  the  kiln.  Though  at  present  used  for  the  man- 
ufacture of  soft-mud  bricks  and  burnt  in  up-draft  kilns, 
this  process  does  not  do  the  clay  justice  and  does  not  bring 
eut  its  best  colors,  as  a  down-draft  kiln  would  do.  It  vit- 
rifies between  cones  3  and  1.  When  burnt  at  a  lower  tem- 
perature it  produces  a  fine  red  color. 

It  has  been  realized  from  experience  that  both  weath- 
ering and  thorough  air  drying  help  considerably  in  over- 
coming the  difficulties  encountered  in  the  use  of  this  clay. 
Hence,  by  allowing  it  to  freeze  through  the  winter  it  would 
become  quite  workable  in  the  spring.  The  difficulty  is, 
however,  in  being  sure  that  all  of  the  clay  has  been  suffi- 
ciently weathered,  and  though  the  drying  loss  may  be  re- 
duced, some  loss  in  burning  may  still  be  found  to  occur. 
the  same  thing  applying  to  the  air  drying. 

Considering  the  benefit  derived  from  air  drying,  it  was 
proposed  to  carry  this  process  further  and  to  dry  the  clay 
at  higher  temperatures.  For  this  purpose  a  sample  was 
taken  from  that  part  of  the  bank,  used  by  the  Sheldon 
Brick  Company,  that  had  given  the  most  trouble. 

In  the  preliminary  work,  small  samples  of  this  clay 
were  dried  in  a  laboratory  air  bath  at  100,  200  and  300°C. 
These  were  then  pulverized,  passed  through  an  eight  mesh 
screen,  tempered,  wedged  and  pressed  into  bars,  10"  x  |" 
x  i/o"  in  a  brass  mould.  A  portion  of  the  undried 
clay  was  also  wedged  and  pressed  in  the  same  mould. 
After  drying  in  the  air  at  ordinary  temperature  the  linear 
shrinkages  were  determined.  It  was  found  that  the  bar 
made  from  the  undried  clay  warped  very  badly  as  well  as 
the  bar  made  from  the  clay  dried  at  100°,  but  that  the  bars 
moulded  from  the  clay  dried  at  200°  and  300°  showed  very 
little  warping. 


The  linear  shrinkages  were  as  follows: 

Undried  Clay  _10.3  Per  cent, 

Clay  dried  at  100  ..... 9.7     "         " 

Clay  dried  at  200  7.3     " 

("lav  dried  at  300°.. 7.1     " 

In  tempering  the  dried  clay  it  was  observed  that  the 
sample  dried  at  100  still  possessed  the  sticky  nature  of 
the  undried  clay,  while  the  charge  dried  at  200°  had  lost  to 
a  very  large  extent  this  characteristic  property.  At  the 
same  time  a  certain  granular  appearance  was  noticed  as 
well  as  a  slight  change  in  color  from  yellow  to  reddish. 
The  sample  dried  at  300  worked  practically  the  same  as 
I  he  one  heated  to  200°.  Hence,  it  was  obvious  that  what- 
ever changes  had  taken  place  in  the  structure  of  the  clay 
occurred  at  aboul  200  <\  and  this  was  the  temperature 
chosen  in  tin1  work  that  followed. 

In  order  to  bring  out  the  changes  caused  by  this  dry- 
ing treatment,  still  further  experiments  were  made.  A 
sample  of  the  undried  clay  was  taken  and  divided  into  two 
parts.  One-half  was  dried  at  200°  in  a  laboratory  oven,  the 
other  half  was  left  as  it  was.  Both  of  these  batches  were 
placed  in  porcelain  jar  mills  of  one  gallon  size,  together 


Trfins. 

Rm.  CtR  Soc.  VolSI  . 

Dle 

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D^lfrD  AT    £00 °C           \ 

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UrBONR   JoiHT    Gl_RY.    UNDRItO. 

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Df?\SrD   PiT    200° C. 

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with  sufficient  distilled  water  to  make  a  fairly  thick  slip, 
and  ground  for  one  hour.  The  grinding  action  of  these 
small  mills  is  very  slight  so  that  the  fineness  of  grain  was 
affected  hut  little.  Each  of  the  two  slips  was  passed 
through  an  80  mesh  sieve. 

The  viscosity  of  each  of  the  slips  was  then  determined 
by  means  of  n  Coulomb  viscosimeter  which  had  been  con- 
structed in  the  Department  of  Ceramics,  University  of  Illi- 
nois, for  the  purpose  of  studying  clay  slips,  as  described  in 
Vol.  X,  Trans.  Am.  Ceramic  Society. 

The  amount  of  (day  held  in  suspension  in  the  slips  was 
determined  by  evaporating  the  slips  to  dryness  and  weigh- 
ing in  small  metal  pans.  In  order  to  obtain  the  viscosities 
<>f  lower  concentrations,  the  slips  were  diluted  with  water, 
thoroughly  stirred  up  and  tested  as  before. 

In  the  accompanying  curves  we  observe  clearly  what 
great  changes  have  been  brought  about  by  the  drying  treat- 
ment. It  is  evident  that  this  change  involves  the  structure 
of  the  colloidal  portion  of  the  clay,  since  naturally  neither 
the  size  of  grain  was  altered  nor  anything  added  to  or  sub- 
tracted from  the  (day  in  drying.  Just  how  long  a  time 
would  be  required  to  bring  back  the  clay  to  its  original 
state  of  viscosity,  if  this  is  possible  at  all,  would  be  an 
interesting  question. 

We  observe  from  the  curves  that  for  instance  in  the 
case  of  the  fresh  (day  a  viscosity  of  1.18  is  reached  with 
20%  of  clay,  while  for  the  same  viscosity  35%  of  the  dried 
(day  is  required.  The  latter  therefore  shows  a  marked  de- 
crease in  the  viscosity  characteristic  of  plastic  clays. 

In  order  to  bring  out  the  differences  between  the  un- 
dried  and  the  dried  clay  still  further,  another  series  of 
tests  was  made  by  taking  these  (days  alone  and  in  several 
proportions  and  making  them  up  into  round  discs,  3*4  in- 
in  diameter  and  7/8  in.  thick.  For  this  purpose  the  fresh 
clay  was  thoroughly  wedged,  while  the  dry  clay  was  pul- 
verized and  passed  through  a  10  mesh  screen,  made  up  with 
water  and  tempered.  The  discs  were  made  by  batting  the 
clay  into  a  slab  between  two  guides  and  passing  a  roller 
over  the  latter  so  as  to  obtain  uniform  thickness.  The 
slabs  were  then  cut  into  discs  by  means  of  a  tin  biscuit 
cutter  and  when  sufficiently  stiff  they  were  repressed  on  a 


hand  screw  press  provided  with  a  corresponding  round  die. 
Ten  trials  of  each  serif's  were  placed  in  a  Seger  volnmino- 
meter  and  the  volume  determined  by  displacement  in  kero- 
sene after  having  been  immersed  in  petroleum  for  24  hours. 
The  same  process  was  repeated  after  the  discs  were  dry. 
The  average  of  ten  determinations  was  taken  as  the  drying 
shrinkage.  The  dry  test  pieces  were  all  placed  in  a  Caul- 
kins  mnftie  kiln,  tired  with  oil  and  burnt  to  cone  4,  this 
temperature  having  previously  been  determined  as  the  best 
maturing  point  of  the  clay.  Each  of  the  ten  trial  pieces  of 
the  several  series  which  had  been  measured  for  drying 
shrinkage,  was,  after  burning,  again  placed  in  the  volu- 
lninometer  and  the  volume  determined.  The  balance  of 
the  trials  were  placed  in  water  with  one  face  exposed  and 
allowed  to  stand  for  48  hours,  this  period  of  time  having 
been  established  as  the  point  beyond  which  practically  no 
farther  absorption  took  place.  They  were  then  divided 
into  classes  according  to  the  absorption  found. 

At  the  same  time  discs  were  made  in  similar  manner 
from  (Jalesbnrg  shah-  which,  however,  were  tired  at  cone  2, 
the  best  temperature  for  this  material.  The  results  of  this 
work  are  collected  in  the  following  tables,  the  shrinkage 
being  expressed  by  per  cent  in  volume.  The  percentages  of 
loss  are  based  upon  200  discs  made  from  the  undried  Ur- 
bana clay,  200  of  the  dried  Urbana  clay,  and  125  discs  of 
A,  15,  and  C. 


Kind  of  Material 

>> 

S  -a 

u  .a 

c 

11 
P 

bo 

~  a 
(J  oo 

(S    cs 

-    I* 

p  ~ 

Urbana  Clay 
25%  dried, 
75%  undried 

Urbana  Clay 

50%  dried, 

50%  undried 

0.2"E 

it 
u 

|| 

6  sz 

o 

MARK 

u 

ID 

A 

B 

c 

G 

Amount  of  tempering  water,  in 

%  of  dry   \vt 

33.5 

29.9 

32.0 

31.9 

31.0 

Drying  Shrinkage  in   %,  by  vol.... 

41.2 

29.3 

39.1 

35.8 

34.1 

7.5 

Burning  Shrinkage  in  %,  by  vol... 

21,1 

20.6 

21.0 

21.0 

20.9 

16.2 

32.0 

0.5 

26.0 

15.3 

9.7 

Burning  loss   in    ,r} - 

1.3.0 

4.0 

9.1 

11.0 

12.9 

2.5 

Total   loss   in   % 

47.(1 

4.5 

35.1 

26.3 

22.6 

2.5 

From  these  results  it  is  apparent  that  the  pre-heating 
of  the  day  has  greatly  decreased  the  drying  shrinkage,  the 
difference  being  11.9  per  cent  in  volume  or  nearly  4  per  cent 
in  linear  shrinkage,  assuming  for  practical  purposes  that 
the  linear  shrinkage  is  one-third  of  that  in  volume.  A  cur- 
ious fact  is  also  the  decreased  burning  shrinkage,  so  that 
the  total  shrinkage  is  decreased  from  62.3%  by  volume  to 
49.9$  ,  resulting  in  a  difference  of  12.4%.  Or,  expressed 
in  linear  dimensions,  the  decrease  in  total  shrinkage  is 
from  20.7%  to  16.6%.  The  loss  in  drying  which  took  place 
in  the  open  laboratory  at  ordinary  room  temperature  has 
been  decreased  from  32.0  to  0.5%,  a  gain  of  31.5%.  The 
gain  in  burning  loss  was  11%'  and  in  the  total  loss  42.5%. 

As  to  the  mixtures  of  preheated  and  undried  clay,  we 
observe  that  the  shrinkage  and  losses  decrease  roughly 
with  the  increase  of  preheated  clay  and  thus  these  results 
verify  the  observations  on  the  preheated  clay  itself. 

Since  there  is  a  possibility  from  the  practical  stand- 
point of  the  drying  and  burning  losses  that  the  same  re- 
sults would  be  obtained  by  the  addition  of  sand  to  the  clay, 
a  short  series  was  carried  through  in  which  5,  10  and  15% 
of  sand  passing  the  8-mesh  sieve  were  added  to  the  undried 
Urbana  clay.  Of  each  sand  mixture  125  discs  were  made. 
The  results  of  this  work  are  collected  in  the  following  table 
in  which  the  data  for  the  undried  and  the  preheated  clay 
are  repeated  for  the  sake  of  comparison : 


Kind  of  Material 


U 


.2  —  « 

a  j-  o  & 


'*>1« 


§2 


'^.5  5 


MARK  |     U 

Amount   of  tempering  water,  in   % 

of    dry    \vt |    33.5 

Drying  Shrinkage  in  %,  by  vol |   41.2 

I 
Burning  Shrinknge  in  %,  by  vol |   21.1 

Drying  loss   in   % |    32.0 

I 
Burning  loss  in  % |    15.0 

I 
Total    loss   in    % |   47.0 


UD 


1) 


F 


29.9 
29.3 


32.0 
39.1 


20.0    |  20.2 

I 

0.5    !  6.1 

4.0    |  11.3 

I 

4.5    I  17.4 


31.5 

37.6 

19.3 

5.2 

33.0 
38.2 


31.1 

35.2 
18.0 
5.0 
42.0 
47.0 


From  these  results  we  observe  that  the  drying  shrink- 
age has  been  decreased  somewhat  ami  the  drying  loss  a 
good  deal,  roughly  by  about  25%.  The  burning  shrinkage 
also  has  been  reduced,  but  unfortunately  the  burning  loss, 
though  showing  an  improvement  in  the  .V,  sand  mixture, 
increased  very  rapidly  with  more  sand.  As  compared  with 
the  total  loss  of  the  preheated  clay,  the  gain  has  been  but 
small  and  at  least  as  far  as  the  sand  used  was  concerned 
this  remedy  offers  but  little  hope  for  practical  improve- 
ment since  the  losses  arc  still  too  great.  Tin1  advantage  of 
preheating  this  joint  clay  is  seen  from  the  small  loss  in  dry- 
ing and  burning.  An  explanation  of  the  ineffectiveness  of 
the  sand  mixture  perhaps  is  due  to  the  fact  that  the  clay 
itself  is  not  changed  in  its  physical  properties  and  we  have 
here  simply  a  case  of  dilution.  With  larger  amounts  of 
sand  we  also  have  in  burning  certain  volume  changes 
which  appear  to  be  opposed  to  each  other,  so  that  strains 
are  produced  which  result  disastrously. 

In  order  to  show  whether  the  Urbana  joint  clay  after 
having  been  burnt  apparently  to  a  sound  body  really  was 
free  from  incipient  checking,  it  was  determined  to  make 
rattler  tests.  For  this  purpose  the  burnt  discs,  tree  from 
flaws,  were  first  graded  according  to  their  water  absorp- 
tion and  compared  with  discs  made  from  Galesburg  shale 
which  had  burnt  to  the  best  degree  of  maturity. 

The  rattler  test  was  made  in  a  Scheibell  mill,  consist- 
ing of  a  chilled  iron  receptacle,  elliptical  in  cross  section, 
with  a  long  axis  23  in.  in  length  and  a  short  axis  of  7y2 
in.,  revolving  31  revolutions  per  minute.  The  rattler  was 
first  standardized  with  a  mixture  of  iron  jackstones  in  the 
shape  of  I1  4  in.  cubes  weighing  on  an  average  0.9  pound 
and  Iceland  pebbles  with  an  average  length  of  3%  in-  and 
a  width  of  2%  in.  The  average  weight  was  0.7  pound.  In 
the  standardization  the  Galesburg  discs  were  used, 
five  of  them  in  a  charge  which  weighed  about  2.2  pounds. 
The  combination  giving  the  most  constant  results  was  used 
for  the  comparative  tests  of  the  joint  clay  discs  with  the 
Galesburg  test  pieces.  In  each  case  the  results  were 
checked.  Finally,  two  charges  were  used,  2-C,  containing 
75  pounds  of  pebbles  and  50  pounds  of  jackstones  and  2-D, 


consisting  of  100  pounds  of  pebbles  and  50  pounds  of  jack- 
stones.  In  using  charge  2-C  the  mill  was  about  %  full 
and  with  2-1)  it  was  y~  full.  The  time  of  running  was  one 
hour.  It  was  found  that  2-<  1  was  a  more  severe  charge  than 
2-D  on  account  of  the  element  of  impact  introduced  by  the 
mill  being  less  full. 

The  rattler  losses  are  tabulated  as  follows : 


All  disc*  apparently  perfect  and  shown 
an  absorption  of  195    and  less 

g 

2- 

%  1 

-C 

2- 

-D 

%  Loss 

( ialesburg    shale,    G 



9.S 

9.7 

5.5 

5 

5 

Urbana  clav,  preheated,  U.   D 



12.3 

12.8 

4.0 

4 

5 

14.7 

14.5 

5.0 

25$  preheated  &  75 9?  undried  Urbana  clay, 

\ 

11.5 





509?  preheated  &  509?  undried  Urbana  clay, 

B 

11.8 



7595  preheated  &  25 95  undried  Urbana  clay 
9595    undried  Urbana  clay,     595    sand.  1)  .. 

CI 

11.8 

12.5 
12..1 



5.9 
(1.2 

9095    undried  Urbana  clay,  109$   sand.  K 



8595    undried  Urbana  clay,  1595    sand.   F 

14.1 

7.4 



These  results  show  plainly  that  preheating  has  im- 
proved the  resistance  of  the  joint  clay  to  abrasion  decid- 
edly, not,  of  course,  due  to  any  change  affecting  the  min- 
eral and  chemical  structure  of  the  (day  itself,  but  to  the 
elimination  of  drying  defects,  incipient  cracks  and  strains 
caused  in  drying.  If  it  were  possible  to  dry  tin1  fresh  (day 
without  injury  it  would  possess  the  same  resistance  to  ab- 
rasion exhibited  by  the  preheated  material.  The  Urbana 
clay  is  evidently  more  brittle  than  tin1  Galesburg  shale,  but 
it  is  harder,  due  to  the  fineness  of  grain  of  the  joint  clay. 
One  might  venture  to  say,  judging  from  the  above  compari- 
son, that  the  latter  could  probably  be  used  as  a  paving 
material  for  streets  which  are  not  subject  to  heavy  travel, 
provided,  however,  that  the  clay  would  correspond  uni- 
formly to  the  sample  tested  in  this  work,  which  is  some- 
what questionable  in  the  case  of  glacial  deposits. 


The  addition  of  sand,  according  to  the  above  results, 
contributes  nothing  to  the  resistance  to  abrasion,  though 
it  shows  an  improvement  over  the  undried  (day  by  lessen- 
ing the  checking  in  drying. 

CONCLUSIONS. 

From  the  results  of  this  work  it  is  evident  that  the 
faults  of  the  joint  (day  have  been  overcome  by  this  pre- 
liminary drying  treatment  at  200°C.  The  sticky 
nature  of  the  clay  has  been  destroyed,  tin1  drying 
shrinkage  reduced  greatly  and  the  burning  shrinkage 
partly,  while  the  losses  in  drying  have  been  practically 
eliminated  and  The  burning  loss  lowered  most  decidedly. 
If,  therefore,  this  preheating  can  be  carried  on  econom- 
ically in  properly  constructed  dryers,  either  tired  directly 
or  making  use  of  the  waste  heal  of  kilns,  the  treatment 
thus  suggested  ought  to  find  more  extensive  practical  ap- 
plication. 

At  the  same  time  there  must  be  remembered  that  the 
dry  clay  can  be  disintegrated  and  screened  more  cheaply 
than  the  clay  coming  wet  from  the  bank,  thus  enabling  the 
manufacturer  to  remove  the  impurities,  such  as  gravel, 
lime,  pebbles  and  other  mineral  detritus,  which  are  espe- 
cially liable  to  be  present  in  the  glacial  clays,  more  cheaply 
and  thoroughly,  besides  making  the  operator  independent 
of  weather  conditions.  Also  it  is  thus  possible  to  produce 
wares  of  a  higher  grade  from  low  grade  material  and  in 
districts  where  other  clays  are  lacking.  Tt  is  self-evident 
that  the  increased  cost  of  production  caused  by  this  treat- 
ment may  be  prohibitory  in  localities  where  it  is  possible 
to  find  (days  which  do  not  require  this  kind  of  preparation. 
The  matter  of  the  preliminary  drying  of  clay  is  not  new, 
but  the  changes  brought  about  by  it  have  not  been  clearly 
recognized  and  its  importance  in  certain  cases  not  consid- 
ered. It  ought  to  lie  especially  applicable  for  higher 
grades  of  ware  such  as  roofing  tiles,  hollow  ware,  terra 
cotta,  etc. 

In  regard  to  the  cost  of  drying  clays  by  the  rotary 
dryer,  which  is  the  most  efficient  apparatus  for  this  pur- 
pose, some  data  have  been  obtained  from  two  firms,  A  and 
P.. 


Firm  A  recommends  a  rotary  dryer,  heated  by  direct 
Siring,  <><>  in.  in  diameter  and  If!  ft.  long.  This  aparatus 
is  encased  in  brick.  The  clay  is  fed  automatically  and  at 
a  constant  rate,  this  being  very  important.  About  35,000 
common  and  from  5,000  to  6,000  fire  brick  are  required  in 
the  construction.  The  total  weight  of  the  dryer  is  about 
40  tons.  The  cost  of  the  dryer,  complete,  is  $3000,  to 
which  the  freight  is  to  be  added.  This  machine  will  dry 
15  tons  of  clay  per  hour.  It  will  require  8 — 12  horse- 
power to  operate  and  for  a  material  containing  15rr  <>f 
moisture  the  fuel  consumption  would  be  about  500  pounds 
of  coal  per  hour,  at  the  rate  of  15  tons  of  clay  for  the  same 
length  of  time.  Including  labor  and  depreciation  the  cost 
of  drying  is  estimated  at  10  cents  per  ton. 

The  firm  B  estimates  the  cost  of  the  dryer  to  be  $3,500 
and  cost  of  erection  at  $600.  The  power  required  is  20 
horse-power  and  the  fuel  consumption  60  pounds  of  good 
(  oal  per  ton  of  bank  clay.  The  cost  of  drying  is  estimated 
to  be  12  cents  per  ton  of  bank  (day. 

In  this  connection  we  must  remember  also  that  the 
size  of  the  brick  moulds,  etc.,  must  be  reduced  in  order  to 
correspond  to  the  decreased  shrinkage  of  the  preheated 
clay,  though  this  do;>s  not  mean  that  a  saving  is  effected. 

Further  work  is  necessary  to  determine  to  what  ex- 
tent this  method  may  be  applied  to  materials  other  than 
the  joint  clay  discussed  in  these  tests. 

Practically  all  the  laboratory  work  of  this  investiga- 
tion was  done  by  the  junior  writer,  Mr.  F.  E.  Layman,  the 
senior  writer  having  planned  the  experiments  and  assisted 
in  writing  up  the  results.  The  means  for  carrying  on  the 
tests  were  furnished  by  the  Ceramic  Department  of  tin1 
University  of  Illinois,  through  Prof.  C.  W.  Rolfe,  the 
director. 


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